Diet can affect levels of the anabolic hormone testosterone in the blood during prolonged strength training, according to a new study from Finland. Specifically, diets with insufficient fat and/or excessive protein may compromise the anabolic hormone environment over the course of a training programme.

The relationship between dietary intake and serum (blood) anabolic hormone concentrations of testosterone, free testosterone and growth hormone were examined at rest as well as after heavy-resistance exercise (HRE) in eight strength athletes and 10 physically active non-athletes.

According to the subjects’ food diaries, the strength athletes ate significantly more protein and less monounsaturated fatty acids than the non-athletes, although there were no significant between-groups differences in energy, carbohydrate and total fat intake.

Significant relationships between nutrient intake and serum basal testosterone levels were apparent in the strength athletes only. When the data were analysed, both protein:fat and protein:carbohydrate ratios correlated negatively with serum basal testosterone levels, although there were no significant relationships between nutrient intake and serum basal free testosterone or growth hormone concentrations.

After heavy resistance exercise, serum anabolic hormone concentrations were significantly elevated in both experimental groups, with the highest response observed in serum growth hormone levels, which showed an increase as large as 50,000% 15 minutes afterwards. The relative responses of serum testosterone to the loading were highest in the strength athletes.

Significant positive correlations between nutrient intake and serum total and free testosterone responses to HRE were observed with regard to total fat, saturated fatty acids and monounsaturated fatty acids, while negative correlations were observed with dietary protein, protein:fat, carbohydrate:fat and protein: carbohydrate ratios.

The researchers conclude that: ‘Diets with insufficient fat and/or excessive protein may compromise the anabolic hormonal environment over a training programme. The present nutritional data in relation to serum basal testosterone concentration and serum total and free testosterone responses to HRE suggest that the moderate intake of both fat and protein could be recommended for strength athletes.’

Int J Sports Med 2004; 24:627-633